(1) Field of the Invention
The present invention belongs to a fluid flow rate detection technology, and particularly relates to a flow rate sensor and flow rate detecting apparatus for detecting the flow rate of fluid flowing in a pipe line, and to a temperature sensor for detecting temperature of fluid when detecting the flow rate thereof. The flow rate sensor of the present invention is suitably used to accurately measure the flow rate of fluid under various temperature conditions and to make it easy to fabricate the flow rate sensor.
Further, the present invention particularly intends to improve the measurement accuracy of the flow rate sensor, flow rate detecting apparatus and temperature sensor.
(2) Description of Related Art
Various types of sensors have been hitherto used as a flow rate sensor (or flow velocity sensor) for measuring the flow rate (or flow velocity) of various fluid, particularly liquid, and a so-called thermal (particularly indirectly heated type) flow rate sensor is used because the cost can be easily reduced.
A sensor in which a thin-film heating element and a thin-film temperature sensing element are laminated through an insulating layer on a substrate and the substrate is secured to a pipe line is used as an indirectly heated type flow rate sensor, so that the substrate and the fluid in the pipe line are thermally contacted to each other. By passing current through the heating element, the temperature sensing element is heated to vary the electrical characteristic of the temperature sensing element such as the value of the electrical resistance of the temperature sensing element. The electrical resistance value (varied on the basis of the temperature increase of the temperature sensing element) is varied in accordance with the flow rate (flow velocity) of fluid flowing in the pipe line. This is because a part of the heating value of the heating element is transferred through the substrate into the fluid, the heating value diffusing into the fluid is varied in accordance with the flow rate (flow velocity) of the fluid, and the heating value to be supplied to the temperature sensing element is varied in accordance with the variation of the heating value diffusing into the fluid, so that the electrical resistance value of the temperature sensing element is varied. The variation of the electrical resistance value of the temperature sensing element is also varied in accordance with the temperature of the fluid. Therefore, a temperature sensing device for temperature compensation is installed in an electrical circuit for measuring the variation of the electrical resistance value of the temperature sensing element to suppress the variation of the flow-rate measurement value due to the temperature of the fluid at maximum.
An indirectly heated type flow rate sensor using thin film elements as described above is disclosed in JP-08-146026(A), for example.
The conventional indirectly heated type flow rate sensor has a metallic pipe line to be connected external pipe lines. The fluid flows in the pipe line, which is exposed to the outside. Since the metallic pipe line has high thermal conductivity, the temperature variation of the environmental atmosphere is easily transmitted to the fluid in the pipe line, especially to the fluid at the vicinity of inner wall of the pipe line, resulting in lowering the accuracy of detection of the flow rate by the thermal flow rate sensor, especially in case of small amount of flow rate. Such a problem is significant when the difference between the temperature of the fluid flowing through the pipe line and the environmental temperature is great.
The conventional indirectly heated type flow rate sensor is attached to the external pipe line so that the substrate of a flow rate detector or a casing which is thermally connected to the substrate is exposed from the wall surface of the pipe line to the fluid.
For example, the indirectly heated type flow rate sensor disclosed in the above JP-08-146026(A) as the sensor of high thermal response, high measuring accuracy, small size and producibilty with low cost has the following construction:
As shown in FIGS. 31A and 31B, a flow rate sensor 501 is composed of a thin film heating element 503, thin film temperature sensing element 504 laminated via an insulating layer 505 on a substrate 502, and attached to an appropriate portion of a pipe line 506 as shown in FIG. 32 in application.
In the flow rate sensor 501, the temperature sensing element504 is heated by supplying electric power to the heating element 503, and the change of the electric resistance value in the temperature sensing element is detected. The flow rate sensor 501 is disposed on the pipe line 506, and therefore a part of the heating value of the heating element 503 is transferred through the substrate 502 into the fluid flowing through the pipe line. The heating value transferred to the temperature sensing element 504 amounts to the heating value generated by the heating element subtracted with the heating value diffusing into the fluid, which is varied in accordance with the flow rate of the fluid. Therefore, the flow rate of the fluid flowing through the pipe line 506 can be detected by detecting the electrical resistance value of the temperature sensing element which is varied in accordance with the heating value to be supplied to the temperature sensing element 504.
The dispersing heating value is also varied in accordance with the temperature of the fluid, and therefore as shown in FIG. 32, a temperature sensor 507 is arranged on an appropriate portion of the pipe line 506, and electrical resistance value of the temperature sensing element is also varied in accordance with the temperature of the fluid. Therefore, a temperature sensing device for temperature compensation is installed in an electrical circuit for measuring the variation of the electrical resistance value of the temperature sensing element to suppress the variation of the flow-rate measurement value due to the temperature of the fluid at maximum.
However, since the conventional flow rate sensor 501 is directly connected to the metallic pipe line 506 which is exposed to the outside, the heating value posessed by the fluid is dissipated to the outside or the heating value is supplied to the fluid through the metallic pipe line 506 having high thermal conductivity, resulting in that the detection accuracy of the flow rate sensor 501 is lowered. The influence of such heat dissipation on the detection accuracy of the flow rate sensor is significant when the flow rate of the fluid is very small, and more significant when the specific heat of the fluid is small.
When the fluid is viscous fluid, particularly viscous fluid having relatively high viscosity, particularly liquid, the flow-velocity distribution on the section perpendicular to the flow of the fluid in the pipe line 506 is more remarkable so as to show a parabolic curve having an extreme value at the central portion, that is, the flow-velocity at the central part greatly didders from the flow velocity at the vicinity of the wall of pipe line. In the case of the conventional sensor in which the substrate 502 or the casing 508 connected to the substrate is merely exposed to the fluid at the wall of the pipe line, the flow-velocity distribution has a great effect on the precision of the flow-rate measurement. This is because the flow velocity of the fluid flowing at the center portion on the section of the pipe line is not taken into consideration, but only the flow velocity of the fluid in the neighborhood of the wall of the pipe line is taken into consideration. As described above, the conventional flow rate sensor has such a problem that it is difficult to measure the flow rate of fluid accurately when the fluid is viscous fluid having relatively high viscosity.
Even when fluid has low viscosity at room temperature, it induces a problem connected to the above viscosity problem because the viscosity of the fluid increases as the temperature is lowered.
Further, the above problem is more remarkable when the flow rate per unit time is relatively low than when the flow rate per unit time is high.
In order to improve the detection accuracy of the indirectly heated type flow rate sensor, it is important to transmit the heat value generated by the heater to the temperature sensor under the influence of only the heat absorption by the fluid. In the conventional indirectly heated type flow rate sensor, however, the heat transmission between the environment and the temperature sensor or heater cannot be ignored as mentioned in the above, and the detected flow rate value is varied in accordance with the environmental temperature, resulting in occurrence of the error in the flow rate detection.
The flow rate sensor is required to be used under an extremely broad temperature environment in accordance with a geographical condition, an indoor or outdoor condition, etc. Further, these conditions are added with a season condition, a day or night condition, etc., and the temperature environment is greatly varied, especially in the outdoor condition. Therefore, there has been required a flow rate sensor which can detect the flow rate accurately under such a broad environmental temperature condition as described above.
Therefore, an object of the present invention is to provide a flow rate sensor or flowmeter which can accurately measure the flow rate of fluid on by preventing the influence of the environmental temperature condition on the measuring accuracy.
Further, an object of the present invention is to make it easy to fabricate the thermal flow rate sensor or flowmeter.
Further, an object of the present invention is to provide a flow rate sensor or flowmeter which can accurately measure the flow rate of fluid flowing in a pipe line even when the fluid is viscous fluid having relatively high viscosity.
Further, an object of the present invention is to provide a flow rate sensor or flowmeter which can accurately measure the flow rate of fluid flowing in a pipe line even when the flow rate is relatively small.
Still further, an object of the present invention is to provide a flow rate sensor or flowmeter which can accurately measure the flow rate of fluid even when the specific heat is small or the flow rate is small by reducing the heating value dissipated from the flow rate sensor to the casing or the outside.
Further, an object of the present invention is to provide a flow rate sensor or flowmeter which can be attached easily to the casing to be stably fixed thereto and has sufficient durability.
Further, an object of the present invention is to provide a temperature sensor for use in measuring the flow rate of the fluid, which has the construction similar to the flow rate sensor and can accurately measure the flow rate of fluid by reducing the heat transmission between the environmental atmosphere and the temperature sensor.
In order to attain the above object, according to the present invention, there is provided a flow rate sensor comprising:
a flow rate detector having a heating function and a temperature sensing function;
a pipe line for fluid to be detected which is formed so that heat from the flow rate detector is transferred to and absorbed by the fluid, wherein the temperature sensing which is affected by a heat absorption effect of the fluid due to the heat is executed in the flow rate detector, and the flow rate of the fluid in the pipe line is detected on the basis of the temperature sensing result;
at least one unit retaining portion formed on a casing in which the pipe line is formed, the unit retaining portion being disposed adjacent to the pipe line; and
a flow rate detecting unit comprising said flow rate detector and retained by the unit retaining portion.
In an aspect of the present invention, the casing is made of synthetic resin.
In an aspect of the present invention, the flow rate detecting unit comprises said flow rate detector, a first heat transfer member provided to the flow rate detector, a first electrode terminal electrically connected to the flow rate detector and a first base portion made of synthetic resin, the first base portion is retained by the unit retaining portion, the first heat transfer member extends from the first base portion into the pipe line, and the first electrode terminal extends from the first base portion to the opposite side to the pipe line.
In an aspect of the present invention, the first heat transfer member extends to at least the vicinity of the central portion on the section of the pipe line.
In an aspect of the present invention, the first base portion comprises an inner portion having elasticity and an outer portion disposed around the inner portion.
In an aspect of the present invention, a cavity is formed in a central portion of the first base portion.
In an aspect of the present invention, the first heat transfer member has a plate form, and the flow rate detector is joined to a portion of the first heat transfer member located in the first base portion.
In an aspect of the present invention, a seal member for the pipe line is interposed between the first base member and the casing.
In an aspect of the present invention, a device accommodating portion is formed in the casing at the outside of the unit retaining portion, a wiring board is disposed in the device accommodating portion.
In an aspect of the present invention, the device accommodating portion is covered by a lid portion.
In an aspect of the present invention, the flow rate detector comprises a thin-film heating element and a flow rate detecting thin-film temperature sensing element disposed so as to be affected by the effect of the heating of the thin-film heating element, the thin-film heating element and the flow rate detecting thin-film temperature sensing element being formed on a first substrate.
In an aspect of the present invention, the first heat transfer member is joined to the first substrate.
In an aspect of the present invention, the thin-film heating element and the flow rate detection thin-film temperature sensing element are laminated on a first surface of the first substrate through a first insulating layer.
In an aspect of the present invention, the first heat transfer member is joined to a second surface of the first substrate.
In an aspect of the present invention, the dimension of the first heat transfer member in the direction of the pipe line is set to be larger than the dimension in the direction perpendicular to the extension direction of the first heat transfer member within the section of the pipe line.
In an aspect of the present invention, the flow rate sensor further comprises a temperature detecting unit retained by the unit retaining portion other than that for retaining the flow rate detecting unit, the temperature detecting unit including a temperature detector for detecting the temperature of the fluid in the pipe line for compensation when the flow rate of the fluid in the pipe line is detected.
In an aspect of the present invention, the temperature detecting unit comprises said temperature detector, a second heat transfer member provided to the temperature detector, a second electrode terminal electrically connected to the temperature detector and a second base portion made of synthetic resin, the second base portion is retained by the unit retaining portion other than that for retaining the flow rate detecting unit, the second heat transfer member extends from the second base portion into the pipe line, and the second electrode terminal extends from the second base portion to the opposite side to the pipe line.
In an aspect of the present invention, the second heat transfer member extends to at least the vicinity of the central portion on the section of the pipe line.
In an aspect of the present invention, the second base portion comprises an inner portion having elasticity and an outer portion disposed around the inner portion.
In an aspect of the present invention, a cavity is formed in a central portion of the second base portion.
In an aspect of the present invention, the second heat transfer member has a plate form, and the temperature detector is joined to a portion of the second heat transfer member located in the second base portion.
In an aspect of the present invention, a seal member for the pipe line is interposed between the second base member and the casing.
In an aspect of the present invention, the wiring board and the second electrode terminal of the temperature detecting unit are electrically connected to each other.
In an aspect of the present invention, the temperature detector comprises a temperature detection thin-film temperature sensing element on the second substrate.
In an aspect of the present invention, the second heat transfer member is joined to the second substrate.
In an aspect of the present invention, the temterature detection thin-film temperature sensing element are laminated on a first surface of the second substrate through a second insulating layer.
In an aspect of the present invention, the second heat transfer member is joined to a second surface of the second substrate.
In an aspect of the present invention, the dimension of the second heat transfer member in the direction of the pipe line is set to be larger than the dimension in the direction perpendicular to the extension direction of the second heat transfer member within the section of the pipe line.
In order to attain the above object, according to the present invention, there is also provided a flow rate sensor comprising:
a flow rate detector having a heating function and a temperature sensing function;
a pipe line for fluid to be detected which is formed so that heat from said flow rate detector is transferred to and absorbed by the fluid, wherein the temperature sensing which is affected by a heat absorption effect of the fluid due to the heat is executed in said flow rate detector, and the flow rate of the fluid in said pipe line is detected on the basis of the temperature sensing result; and
a casing made of synthetic resin.
In order to attain the above object, according to the present invention, there is also provided a flow rate detecting unit or flow rate sensor for use in a flow rate sensor including a flow rate detector having a heating function and a temperature sensing function in which the temperature sensing which is affected by a heat absorption effect of fluid due to the heat is executed and the flow rate of the fluid is detected on the basis of the temperature sensing result, the flow rate detecting unit comprising:
the flow rate detector;
a first heat transfer member provided to the flow rate detector;
a first electrode terminal electrically connected to the flow rate detector; and
a first base portion made of synthetic resin, wherein the first heat transfer member and the first electrode terminal extends to the opposite side to each other.
In order to attain the above object, according to the present invention, there is also provided a fluid temperature detecting unit or fluid temperature sensor for use in a flow rate sensor including a flow rate detector having a heating function and a temperature sensing function in which the temperature sensing which is affected by a heat absorption effect of fluid due to the heat is executed and the flow rate of the fluid is detected on the basis of the temperature sensing result in order to perform compensation of the flow rate detected due to the temperature of the fluid, the temperature detecting unit comprising:
a temperature detector;
a second heat transfer member provided to the temperature detector;
a second electrode terminal electrically connected to the temperature detector; and
a second base portion made of synthetic resin, wherein the second hea t transfer member and the second electrode terminal extends to the opposite si de to each other.
In order to attain the above object, according to the present invention, there is also provided a flow rate sensor comprising:
a flow rate detector having a heating function and a temperature sensing function;
a pipe line for fluid to be detected; and
a flow rate detection heat transfer member which is disposed so as to be affected by heat from the flow rate detector and extends into the pipe line,
wherein the temperature sensing which is affected by a heat absorption effect of the fluid due to the heat via the flow rate detection heat transfer member is executed in the flow rate detector, and the flow rate of the fluid in the pipe line is detected on the basis of the temperature sensing result, and, the flow rate detector and a portion of the flow rate detection heat transfer member thermally connected to the flow rate detector are sealed within a flow rate detection base portion made of synthetic resin having a thermal conductivity of 0.7 [W/m.K] or less.
In an aspect of the present invention, the flow rate detection base portion is made of synthetic resin having a thermal conductivity of 0.4 [W/m.K] or less.
In an aspect of the present invention, the flow rate detection base portion extends in a radial direction of the pipe line and passes through a central axis of the pipe pine.
In an aspect of the present invention, the flow rate detection heat transfer member has a plate form being disposed in the pipe line along the pipe line.
In an aspect of the present invention, the flow rate detector comprises a thin-film heating element and a flow rate detecting thin-film temperature sensing element disposed so as to be affected by the effect of the heating of the thin-film heating element outside the pipe line, the thin-film heating element and the flow rate detecting thin-film temperature sensing element being formed on a first substrate.
In an aspect of the present invention, the flow rate sensor further comprises a fluid temperature detector to perform compensation of the flow rate detected in the flow rate detection, wherein the fluid temperature detector and a fluid temperature detection heat transfer member disposed so as to extend into the pipe line are thermally connected to each other.
In an aspect of the present invention, the flow rate detector and a portion of the temperature detection heat transfer member thermally connected to the flow rate detector are sealed within a temperature detection base portion made of synthetic resin having a thermal conductivity of 0.7 [W/m.K] or less.
In an aspect of the present invention, the temperature detection base portion is made of synthetic resin having a thermal conductivity of 0.4 [W/m.K] or less.
In an aspect of the present invention, the temperature detection base portion extends in a radial direction of the pipe line and passes through a central axis of the pipe pine.
In an aspect of the present invention, the temperature detection heat transfer member has a plate form being disposed in the pipe line along the pipe line.
In an aspect of the present invention, the flow rate sensor further comprising heating control means for controlling the heating of the heating element connected to a passage for supplying electric current to the heating element, wherein the heating control means controls the current to be supplied to the heating element on the basis of the temperature sensing result so that the temperature sensing result is coincident with a target value, and the flow rate of the fluid is detected on the basis of the control state of the heating control means.
In order to attain the above object, according to the present invention, there is also provided a flow rate sensor comprising;
a flow rate detector having a heating element and a temperature sensing element formed on a substrate;
a fin plate for transferring heat to fluid to be detected therethrough, and
an output terminal for outputting the voltage value corresponding to the flow rate, wherein the flow rate detector, a part of the fin plate and a part of the output terminal are coated by molding.
In an aspect of the present invention, the flow rate detector is fixed to an end surface of the fin plate, the flow rate detector and the output terminal are connected to each other via a bonding wire.
In an aspect of the present invention, the fin plate and the output terminal are manufactured by processing a plate to a plate base member and then processing the plate base member to the fin plate and the output terminal.
In an aspect of the present invention, the plate base member is formed by etching the plate.
According to the present invention, there is provided a flow rate detecting apparatus comprising:
the flow rate sensor as described in the above;
a casing having a sensor hole for accommodating the flow rate sensor; and
a fluid flow passage pipe having an opening disposed at a position corresponding to the sensor hole.
In an aspect of the present invention, a seal member is interposed between the flow rate sensor and the sensor hole.
In an aspect of the present invention, the flow rate detecting apparatus further comprising a fluid temperature sensor, wherein a sensor hole for accommodating the temperature sensor is formed in the casing and an opening disposed at a position corresponding to the sensor hole for accommodating the temperature sensor in the fluid flow passage pipe.
In an aspect of the present invention, a seal member is interposed between the temperature sensor and the sensor hole for accommodating the temperature sensor.
According to the present invention, there is provided a flow rate sensor comprising;
a flow rate detector having a heating element and a temperature sensing element formed on a substrate; and
a recess portion formed in the substrate, the recess portion being sealed with an air layer formed therein.
In an aspect of the present invention, the recess portion is formed by etching.
In an aspect of the present invention, the recess portion is sealed by a glass plate.
In an aspect of the present invention, the flow rate sensor further comprises a fin plate performing heat transmission to the fluid, wherein the flow rate detector is fixed to a surface of an end portion of the fin plate so that a side of the flow rate detector on which the heating element and the temperature sensing element is positioned confront the surface of the end portion of the fin plate.
According to the present invention, there is provided a flow rate sensor comprising:
a flow rate detector having a heating element and a temperature sensing element with an insulator interposed therebetween;
a fin plate an end portion of which is joined to the flow rate detector;
an output terminal electrically connected to the flow rate detector; and
a housing made of resin accommodating the flow rate detector,
wherein the fin plate and the output terminal extend to the outside of the housing, a cavity is provided in the housing and the flow rate detector is disposed in the cavity.
In an aspect of the present invention, the end portion of the fin plate joined to the flow rate detector and an end portion of the output terminal connected to the flow rate detector are positioned in the cavity.
In an aspect of the present invention, the end portion of the fin plate joined to the flow rate detector and an end portion of the output terminal connected to the flow rate detector are positioned in the cavity.
In an aspect of the present invention, the end portion of the fin plate joined to the flow rate detector and an end portion of the output terminal connected to the flow rate detector are positioned in the cavity.
In an aspect of the present invention, a notched portion is formed on an outer peripheral surface of the housing.
In an aspect of the present invention, the housing comprises a main body portion having a recess portion and a lid portion covering the recess portion.
According to the present invention, there is also provided a temperature sensor comprising;
a temperature detector having a temperature sensing element and an insulator laminated on the temperature sensing element;
a fin plate an end portion of which is joined to the temperature detector;
an output terminal electrically connected to the temperature detector; and
a housing made of resin accommodating the temperature detector,
wherein the fin plate and the output terminal extend to the outside of the housing, a cavity is provided in the housing and the temperature detector is disposed in the cavity.
In an aspect of the present invention, the end portion of the fin plate joined to the temperature detector and an end portion of the output terminal connected to the emperature detector are positioned in the cavity.
In an aspect of the present invention, a notched portion is formed on an outer peripheral surface of the housing.
In an aspect of the present invention, the housing comprises a main body portion having a recess portion and a lid portion covering the recess portion.